214 CARBONIFEROUS CEPHALOPODA OF IRELAND. 



often with more or less prominent ridges. Siphuncle subccntral in the direction of 

 the periphery to nearly marginal. 

 Carboniferous. 



Group of CfELONAiTiLr^ rj.ANnTWJuATrs. 



40. Cuelouautilus plauotergatus. 41. Ca'louautilus Doobvleusis.* 



42. Coblouautiliis irradus.* 



Genus STKoiiocEiiAs {Hi/att, 1883, emend. 1893). — Shell compressed-di.seoid, with 

 elevated peripheral area and prominent ridges separated by furrows on the sides. 

 Carboniferous. 



Group of Stroboceeas sulcatum. 



43. Stroboceras sulcatum. 44. Stroboceras crassum.* 



Genus Apheleceras {ni/uft, 1883, emend. 1803). — Sliell compre-ssed-discoid. 

 Cross-section subhexagonal. Peripheral area very narrow, sulcated more or less 

 deeply. Umbilical vacuity large ; the first whorl generally completed before the 

 succeeding one touches it. Young shell with lateral and ventral longitudinal ridges. 



Carboniferous. 



Group of Apheleceras mutabile. 



45. Apheleceras mutabile. 4(3. Apheleceras Hiberuicum. 47. Apheleceras trochlea. 



Genus Mesochasmoceuas {Foon], 1900). — Shell discoidal, much compressed. 

 Whorls slowly tapering, narrow, with a very large umbilical vacuity. Cross-section 

 subhexagonal. Periphery slightly cliannelled. No ornamentation at any stage of 

 growth. 



Carboniferous. 



48. Mcsochasmoceras latidorsatuiii. 



Genus DiiiRUoocERAs (IL/att, 1893). — Shell with more compressed whorls than 

 those of Aphdccenis. Periphery channelled. Involution almost complete in tlie 

 adult. (This genus is represented by only one species, and is not satisfactorily 

 defined.) 



Carboniferous. 



45). Diorugoceras plaui<h)rsatum. 



